Field of Technology
The present disclosure relates to a liquid crystal display device, and more particularly, to a liquid crystal display panel having a touch panel and a liquid crystal display device using the liquid crystal display panel.
Discussion of the Related Art
A touch panel is mounted on a display device such as a liquid crystal display device (LCD), a plasma display panel (PDP), an organic light emitting display device (OLED), or an electrophoretic display (EPD).
A method of manufacturing a liquid crystal display device having a touch panel is classified into two types: an add-on type in which a display panel and a touch panel configured to sense touch contacts or operations are separately manufactured and then bonded together, and an in-cell type in which a touch panel is built into or integrated with a display panel.
FIG. 1 is a diagram schematically illustrating a liquid crystal display device according to the related art having an in-cell type touch panel, and FIG. 2 is a diagram illustrating waveforms of signals which are applied to the liquid crystal display device according to the related art having an in-cell type touch panel.
Referring to FIG. 1, the liquid crystal display device according to the related art having an in-cell type touch panel includes a liquid crystal display panel 50 in which touch electrodes, which are also used as common electrodes, are formed. A touch sensing unit 60 drives the touch electrodes, which include driving electrodes TX and receiving electrodes RX. Each of the driving electrodes TX is formed in a line shape and each of the receiving electrodes RX is formed in a line shape or island type jumping line shape. In this case, gate lines are formed in the liquid crystal display device 50 so as to overlap the receiving electrodes RX formed in a horizontal (row) direction of the liquid crystal display device 50.
A common voltage is supplied to the driving electrodes TX and the receiving electrodes RX during an image display period which an image is displayed. Touch drive signals are sequentially supplied to the driving electrodes TX during a touch sensing period in which a touch contact or operation is sensed, and the receiving electrodes RX transmit sensing signals to the touch sensing unit 60.
When the supplied voltages are non-uniform through the driving electrodes and the receiving electrodes, an uneven brightness pattern such as striped patterns having a line shape will be displayed on the screen along the driving electrodes and the receiving electrodes. The striped patterns may be observed by the viewer as dimmed stripes or brightened stripes depend on the voltage deviation.
For example, in the display device illustrated in FIG. 1, the receiving electrodes RX are formed to be parallel to and overlap with the gate lines.
When gate pulses are supplied to the gate lines during the image display period, parasitic capacitance may be generated between the gate lines and the driving electrodes TX and also between the gate lines and the receiving electrodes RX.
As such, a voltage level difference between the common voltage supplied to the driving electrodes TX and the common voltage supplied to the receiving electrodes RX may occur, and a potential difference between pixel voltages charged at pixel electrodes and common voltage charged at common electrode formed on the panel 50 may occur due to the common voltage deviation. Accordingly, vertical striped patterns may appear on the display screen along the driving electrodes TX.
The above-mentioned striped patterns may appear on the screen along the receiving electrodes RX in the horizontal (row) direction.
However, in general, the striped patterns appearing along the driving electrodes TX are more visible due to their arrangement being perpendicular to the gate lines, as opposed to the striped patterns appearing along the receiving electrodes RX which are arranged to be parallel to the gate lines.
As such, if the driving electrodes TX are arranged along the gate lines in the horizontal (row) direction of the liquid crystal display panel 50 and the receiving electrodes RX are arranged to be perpendicular to the gate lines in the vertical (column) direction of the liquid crystal display panel 50, undesirable patterns appearing on the screen in the vertical direction along the receiving electrodes RX may be more conspicuous.
The reason why the striped patterns appear on the liquid crystal display device having an in-cell type touch panel according to the related art will be described below in more detail with reference to FIG. 2.
When a gate pulse GP is supplied to a gate line during the image display period, a data voltage Vdata is supplied to pixels which are corresponding to the gate line and a common voltage Vcom is supplied to the driving electrode TX and the receiving electrode RX. A pixel voltage corresponding to the difference between the data voltage Vdata and the common voltage Vcom is applied to a liquid crystal to control the light transmittance thereof.
When the gate pulse GP falls, the data voltage Vdata and the common voltage Vcom initially fall and then rise again due to a coupling effect. The magnitude of the data voltage Vdata from falling to rising is different from the magnitude of the common voltage Vcom from falling to rising. Accordingly, a pixel voltage Vp1 of an interval in which the gate pulse is in a high state is different from a pixel voltage Vp2 of an interval in which the gate pulse is in a low state.
Referring to FIG. 1, the pixel voltage difference Vp2−Vp1 between the pixels corresponding to the driving electrode TX which is formed to be perpendicular to the gate line is different from the pixel voltage difference Vp2−Vp1 between the pixels corresponding to the receiving electrode RX which is formed to be parallel to the gate line.
A difference in luminance between the pixels corresponding to the driving electrode TX and pixels corresponding to the receiving electrode RX occurs due to the above-mentioned difference, and striped patterns appear in the horizontal (row) or the vertical (column) direction on the liquid crystal display panel 50.
Particularly, since the pixel voltage difference Vp2−Vp1 between the pixels corresponding to the driving electrode TX which is formed to be perpendicular to the gate line is greater than the pixel voltage difference Vp2−Vp1 between the pixels corresponding to the receiving electrode RX which is formed to be parallel to the gate line, the striped pattern appearing on the display screen in the vertical direction perpendicular to the gate line is more conspicuous.